1. Field of the Invention
The present invention relates generally to the field of corn breeding. In particular, the invention relates to inbred corn seed and plants of the variety designated I244225, and derivatives and tissue cultures thereof.
2. Description of Related Art
The goal of field crop breeding is to combine various desirable traits in a single variety/hybrid. Such desirable traits include greater yield, better stalks, better roots, resistance to insecticides, herbicides, pests, and disease, tolerance to heat and drought, reduced time to crop maturity, better agronomic quality, higher nutritional value, and uniformity in germination times, stand establishment, growth rate, maturity, and fruit size.
Breeding techniques take advantage of a plant""s method of pollination. There are two general methods of pollination: a plant self-pollinates if pollen from one flower is transferred to the same or another flower of the same plant. A plant cross-pollinates if pollen comes to it from a flower on a different plant.
Corn plants (Zea mays L.) can be bred by both self-pollination and cross-pollination. Both types of pollination involve the corn plant""s flowers. Corn has separate male and female flowers on the same plant, located on the tassel and the ear, respectively. Natural pollination occurs in corn when wind blows pollen from the tassels to the silks that protrude from the tops of the ear shoot.
Plants that have been self-pollinated and selected for type over many generations become homozygous at almost all gene loci and produce a uniform population of true breeding progeny, a homozygous plant. A cross between two such homozygous plants produces a uniform population of hybrid plants that are heterozygous for many gene loci. Conversely, a cross of two plants each heterozygous at a number of loci produces a population of hybrid plants that differ genetically and are not uniform. The resulting non-uniformity makes performance unpredictable.
The development of uniform corn plant hybrids requires the development of homozygous inbred plants, the crossing of these inbred plants, and the evaluation of the crosses. Pedigree breeding and recurrent selection are examples of breeding methods used to develop inbred plants from breeding populations. Those breeding methods combine the genetic backgrounds from two or more inbred plants or various other broad-based sources into breeding pools from which new inbred plants are developed by selfing and selection of desired phenotypes. The new inbreds are crossed with other inbred plants and the hybrids from these crosses are evaluated to determine which of those have commercial potential.
The pedigree breeding method involves crossing two genotypes. Each genotype can have one or more desirable characteristics lacking in the other; or, each genotype can complement the other. If the two original parental genotypes do not provide all of the desired characteristics, other genotypes can be included in the breeding population. Superior plants that are the products of these crosses are selfed and selected in successive generations. Each succeeding generation becomes more homogeneous as a result of self-pollination and selection. Typically, this method of breeding involves five or more generations of selfing and selection: S1xe2x86x92S2; S2xe2x86x92S3; S3xe2x86x92S4; S4xe2x86x92S5, etc. After at least five generations, the inbred plant is considered genetically pure.
Backcrossing can also be used to improve an inbred plant. Backcrossing transfers a specific desirable trait from one inbred or non-inbred source to an inbred that lacks that trait. This can be accomplished, for example, by first crossing a superior inbred (A) (recurrent parent) to a donor inbred (non-recurrent parent), which carries the appropriate locus or loci for the trait in question. The progeny of this cross are then mated back to the superior recurrent parent (A) followed by selection in the resultant progeny for the desired trait to be transferred from the non-recurrent parent. After five or more backcross generations with selection for the desired trait, the progeny are heterozygous for loci controlling the characteristic being transferred, but are like the superior parent for most or almost all other loci. The last backcross generation would be selfed to give pure breeding progeny for the trait being transferred.
A single cross hybrid corn variety is the cross of two inbred plants, each of which has a genotype which complements the genotype of the other. The hybrid progeny of the first generation is designated F1. Typically, F1 hybrids are more vigorous than their inbred parents. This hybrid vigor, or heterosis, is manifested in many polygenic traits, including markedly improved yields, better stalks, better roots, better uniformity and better insect and disease resistance. In the development of hybrids only the F1 hybrid plants are typically sought. An F1 single cross hybrid is produced when two inbred plants are crossed. A double cross hybrid is produced from four inbred plants crossed in pairs (Axc3x97B and Cxc3x97D) and then the two F1 hybrids are crossed again (Axc3x97B)xc3x97(Cxc3x97D).
The development of a hybrid corn variety involves three steps: (1) the selection of plants from various germplasm pools; (2) the selfing of the selected plants for several generations to produce a series of inbred plants, which, although different from each other, each breed true and are highly uniform; and (3) crossing the selected inbred plants with unrelated inbred plants to produce the hybrid progeny (F1). During the inbreeding process in corn, the vigor of the plants decreases. Vigor is restored when two unrelated inbred plants are crossed to produce the hybrid progeny (F1). An important consequence of the homozygosity and homogeneity of the inbred plants is that the hybrid between any two inbreds is always the same. Once the inbreds that give a superior hybrid have been identified, hybrid seed can be reproduced indefinitely as long as the homogeneity of the inbred parents is maintained. Conversely, much of the hybrid vigor exhibited by F1 hybrids is lost in the next generation (F2) Consequently, seed from hybrid varieties is not used for planting stock. It is not generally beneficial for farmers to save seed of F1 hybrids. Rather, farmers purchase F1 hybrid seed for planting every year.
North American farmers plant tens of millions of acres of corn at the present time and there are extensive national and international commercial corn breeding programs. A continuing goal of these corn breeding programs is to develop corn hybrids that are based on stable inbred plants and have one or more desirable characteristics. To accomplish this goal, the corn breeder must select and develop superior inbred parental plants.
In one aspect, the present invention provides a corn plant of the variety designated I244225. Also provided are corn plants having all the physiological and morphological characteristics of the inbred corn variety I244225. The inbred corn plant of the invention may further comprise, or have, a cytoplasmic or nuclear factor that is capable of conferring male sterility or otherwise preventing self-pollination, such as by self-incompatibility. Parts of the corn plant of the present invention are also provided, for example, pollen obtained from an inbred plant and an ovule of the inbred plant.
The invention also concerns seed of the inbred corn variety I244225. A sample of this seed has been deposited under ATCC Accession No. PTA-4492. The inbred corn seed of the invention may be provided as an essentially homogeneous population of inbred corn seed of the variety designated I244225. Essentially homogeneous populations of inbred seed are those that consist essentially of the particular inbred seed, and are generally free from substantial numbers of other seed, so that the inbred seed forms between about 90% and about 100% of the total seed, and preferably, between about 95% and about 100% of the total seed. Most preferably, an essentially homogeneous population of inbred corn seed will contain between about 98.5%, 99%, 99.5% and about 99.9% of inbred seed, as measured by seed grow outs. This corresponds to current commercial practice among the leading companies in the seed industry.
Therefore, in the practice of the present invention, inbred seed generally forms at least about 97% of the total seed. However, even if a population of inbred corn seed was found, for some reason, to contain about 50/%, or even about 20% or 15% of inbred seed, this would still be distinguished from the small fraction (generally less than 2% and preferably less than 1%) of inbred seed that may be found within a population of hybrid seed, e.g., within a commercial bag of hybrid seed. In such a bag of hybrid seed offered for sale, Federal regulations require that the hybrid seed be at least about 95% of the total seed, or be labeled as a mixture. In the most preferred practice of the invention, the female inbred seed that may be found within a bag of hybrid seed will be about 1% of the total seed, or less, and the male inbred seed that may be found within a bag of hybrid seed will be negligible, i.e., will be on the order of about a maximum of 1 per 100,000, and usually less than this value.
The population of inbred corn seed of the invention can further be particularly defined as being essentially free from hybrid seed. The inbred seed population may be separately grown to provide an essentially homogeneous population of inbred corn plants designated I244225.
In another aspect of the invention, single locus converted plants of variety I244225 are provided. The single transferred locus may preferably be a dominant or recessive allele. Preferably, the single transferred locus will confer such traits as male sterility, yield stability, waxy starch, yield enhancement, industrial usage, herbicide resistance, insect resistance, resistance to bacterial, fungal, nematode or viral disease, male fertility, and enhanced nutritional quality. The single locus may be a naturally occurring maize gene introduced into the genome of the variety by backcrossing, a natural or induced mutation, or a transgene introduced through genetic transformation techniques. When introduced through transformation, a single locus may comprise one or more transgenes integrated at a single chromosomal location.
In yet another aspect of the invention, an inbred corn plant of the variety designated I244225 is provided, wherein a cytoplasmically-inherited trait has been introduced into said inbred plant. Such cytoplasmically-inherited traits are passed to progeny through the female parent in a particular cross. An exemplary cytoplasmically-inherited trait is the male sterility trait. Cytoplasmic-male sterility (CMS) is a pollen abortion phenomenon determined by the interaction between the genes in the cytoplasm and the nucleus. Alteration in the mitochondrial genome and the lack of restorer genes in the nucleus will lead to pollen abortion. With either a normal cytoplasm or the presence of restorer gene(s) in the nucleus, the plant will produce pollen normally. A CMS plant can be pollinated by a maintainer version of the same variety, which has a normal cytoplasm but lacks the restorer gene(s) in the nucleus, and continue to be male sterile in the next generation. The male fertility of a CMS plant can be restored by a restorer version of the same variety, which must have the restorer gene(s) in the nucleus. With the restorer gene(s) in the nucleus, the offspring of the male-sterile plant can produce normal pollen grains and propagate. A cytoplasmically inherited trait may be a naturally occurring maize trait or a trait introduced through genetic transformation techniques.
In another aspect of the invention, a tissue culture of regenerable cells of a plant of variety I244225 is provided. The tissue culture will preferably be capable of regenerating plants capable of expressing all of the physiological and morphological characteristics of the variety, and of regenerating plants having substantially the same genotype as other plants of the variety. Examples of some of the physiological and morphological characteristics of the variety I244225 include characteristics related to yield, maturity, and kernel quality, each of which is specifically disclosed herein. The regenerable cells in such tissue cultures will preferably be derived from embryos, meristematic cells, immature tassels, microspores, pollen, leaves, anthers, roots, root tips, silk, flowers, kernels, ears, cobs, husks, or stalks, or from callus or protoplasts derived from those tissues. Still further, the present invention provides corn plants regenerated from the tissue cultures of the invention, the plants having all the physiological and morphological characteristics of variety I244225.
In yet another aspect of the invention, processes are provided for producing corn seeds or plants, which processes generally comprise crossing a first parent corn plant with a second parent corn plant, wherein at least one of the first or second parent corn plants is a plant of the variety designated I244225. These processes may be further exemplified as processes for preparing hybrid corn seed or plants, wherein a first inbred corn plant is crossed with a second corn plant of a different, distinct variety to provide a hybrid that has, as one of its parents, the inbred corn plant variety I244225. In these processes, crossing will result in the production of seed. The seed production occurs regardless of whether the seed is collected or not.
In a preferred embodiment of the invention, the first step in xe2x80x9ccrossingxe2x80x9d comprises planting, preferably in pollinating proximity, seeds of a first and second parent corn plant, and preferably, seeds of a first inbred corn plant and a second, distinct inbred corn plant. Where the plants are not in pollinating proximity, pollination can nevertheless be accomplished by transferring a pollen or tassel bag from one plant to the other as described below.
A second step comprises cultivating or growing the seeds of said first and second parent corn plants into plants that bear flowers. Corn bears both male flowers (tassels) and female flowers (silks) in separate anatomical structures on the same plant.
A third step comprises preventing self-pollination of the plants, i.e., preventing the silks of a plant from being fertilized by any plant of the same variety, including the same plant. This is preferably done by emasculating the male flowers of the first or second parent corn plant, (i.e., treating or manipulating the flowers so as to prevent pollen production, in order to produce an emasculated parent corn plant), Self-incompatibility systems are also used in some hybrid crops for the same purpose. Self-incompatible plants still shed viable pollen and can pollinate plants of other varieties but are incapable of pollinating themselves or other plants of the same variety.
A fourth step comprises allowing cross-pollination to occur between the first and second parent corn plants. When the plants are not in pollinating proximity, this is done by placing a bag, usually paper or glassine, over the tassels of the first plant and another bag over the silks of the incipient ear on the second plant. The bags are left in place for at least 24 hours. Since pollen is viable for less than 24 hours, this assures that the silks are not pollinated from other pollen sources, that any stray pollen on the tassels of the first plant is dead, and that the only pollen transferred comes from the first plant. The pollen bag over the tassel of the first plant is then shaken vigorously to enhance release of pollen from the tassels, and the shoot bag is removed from the silks of the incipient ear on the second plant. Finally, the pollen bag is removed from the tassel of the first plant and is placed over the silks of the incipient ear of the second plant, shaken again and left in place. Yet another step comprises harvesting the seeds from at least one of the parent corn plants. The harvested seed can be grown to produce a corn plant or hybrid corn plant.
The present invention also provides corn seed and plants produced by a process that comprises crossing a first parent corn plant with a second parent corn plant, wherein at least one of the first or second parent corn plants is a plant of the variety designated I244225. In one embodiment of the invention, corn seed and plants produced by the process are first generation (F1) hybrid corn seed and plants produced by crossing an inbred in accordance with the invention with another, distinct inbred. The present invention further contemplates seed of an F1 hybrid corn plant. Therefore, certain exemplary embodiments of the invention provide an F1 hybrid corn plant and seed thereof. An example of such a hybrid which can be produced with the variety designated I244225 is the hybrid designated 9901499.
In still yet another aspect of the invention, the genetic complement of the corn plant variety designated I244225 is provided. The phrase xe2x80x9cgenetic complementxe2x80x9d is used to refer to the aggregate of nucleotide sequences, the expression of which sequences defines the phenotype of, in the present case, a corn plant, or a cell or tissue of that plant. A genetic complement thus represents the genetic make up of an inbred cell, tissue or plant, and a hybrid genetic complement represents the genetic make up of a hybrid cell, tissue or plant. The invention thus provides corn plant cells that have a genetic complement in accordance with the inbred corn plant cells disclosed herein, and plants, seeds and diploid plants containing such cells.
Plant genetic complements may be assessed by genetic marker profiles, and by the expression of phenotypic traits that are characteristic of the expression of the genetic complement, e.g., isozyme typing profiles. Thus, such corn plant cells may be defined as having an SSR profile in accordance with the profile shown in Table 6, or a genetic isozyme typing profile in accordance with the profile shown in Table 7, or having both an SSR profile and an isozyme typing profile in accordance with the profiles shown in Table 6 and Table 7. It is understood that variety I244225 could also be identified by other types of genetic markers such as, for example, Simple Sequence Length Polymorphisms (SSLPs) (Williams et al., 1990), Randomly Amplified Polymorphic DNAs (RAPDs), DNA Amplification Fingerprinting (DAF), Sequence Characterized Amplified Regions (SCARs), Arbitrary Primed Polymerase Chain Reaction (AP-PCR), Amplified Fragment Length Polymorphisms (AFLPs) (EP 534 858, specifically incorporated herein by reference in its entirety), and Single Nucleotide Polymorphisms (SNPs) (Wang et al., 1998).
In still yet another aspect, the present invention provides hybrid genetic complements, as represented by corn plant cells, tissues, plants, and seeds, formed by the combination of a haploid genetic complement of an inbred corn plant of the invention with a haploid genetic complement of a second corn plant, preferably, another, distinct inbred corn plant. In another aspect, the present invention provides a corn plant regenerated from a tissue culture that comprises a hybrid genetic complement of this invention.
In still yet another aspect, the present invention provides a method of producing an inbred corn plant derived from the corn variety I244225, the method comprising the steps of: (a) preparing a progeny plant derived from corn variety I244225, wherein said preparing comprises crossing a plant of the corn variety I244225 with a second corn plant, and wherein a sample of the seed of corn variety I244225 has been deposited under ATCC Accession No. PTA-4492; (b) crossing the progeny plant with itself or a second plant to produce a seed of a progeny plant of a subsequent generation; (c) growing a progeny plant of a subsequent generation from said seed of a progeny plant of a subsequent generation and crossing the progeny plant of a subsequent generation with itself or a second plant; and (d) repeating steps (c) and (d) for an addition 3-10 generations to produce an inbred corn plant derived from the corn variety I244225. In the method, it may be desirable to select particular plants resulting from step (c) for continued crossing according to steps (b) and (c). By selecting plants having one or more desirable traits, an inbred corn plant derived from the corn variety I244225 is obtained which possesses some of the desirable traits of corn variety I244225 as well potentially other selected traits.